Preheat your oven to 400°F (200°C) and lightly grease the sheet pan with olive oil.
In a mixing bowl, combine the shredded chicken, chili powder, cumin, garlic powder, salt, and pepper. Mix well to evenly coat the chicken with spices.
On the greased sheet pan, place 4 flour tortillas, and evenly spread the chicken mixture on top of each tortilla, leaving a small border around the edges.
Layer the diced bell peppers and red onion over the chicken, then sprinkle the shredded cheese evenly across the top.
Place the remaining 4 flour tortillas on top, gently pressing down to create a layered quesadilla.
Brush the tops of the stacked quesadillas with a little olive oil to help them brown nicely.
Bake in the preheated oven for 15-20 minutes, or until the tortillas are golden brown and the cheese is melted.
Remove from the oven, let cool for a few minutes, then cut into wedges with a sharp knife.
Serve warm with sour cream, salsa, and fresh cilantro, if desired.